Capillary impellers such as a fiber crown rotor, an annular body composed of foam or other materials are known. From an aerodynamic standpoint, these prior art impellers have a structure suitable to provide a grid effect as developed with the vanes of blower rotors. The air cells of a rotating capillary impeller have a conveying effect. Moreover, the capillary impeller through which air may flow, acts as a storage mass, and accordingly, is suitable for the heat exchange between two air currents of different temperature. The heat exchanging effect of a capillary impeller is used for the heat recovery from exhaust air. To this end, heat is removed from absorbed, spent, warm room air and transferred to the outside air region. The heat removed from the exhaust air is supplied to heat the outside air which is blown into the room to be ventilated. Thus, an energy cost-saving results by recovering heat from the exhaust air.
The capillary impeller in a known heat-recovering fan is effective as a heat exchanger and as an air conveyer. This double operation of the capillary impeller does not utilize the maximum heat storage capacity of the material. That is, a compromise must be made between the heat storage capacity, on the one hand, and the air conveying capacity, on the other hand. Such a compromise always calls for certain concessions concerning one factor or the other, and an optimum of heat storage capacity is at the charge of the conveying capacity and vice versa.
Moreover, limits are set to the demand after a compact construction of the blower and undesirably restrict the practical use of the prior art heat-recovering fan. Furthermore, noise problems arise with respect to the air-conveying capillary impeller due to its construction which may also cause further restrictions either in the degree of heat recovery or in its air conveying capacity.